The external thrustbelt of Albania consists of some tectonic zones (Ionian, Kruja and Krasta-Cukali zones), that are westward overthrust, with a large amplitude (50-100 km), above the Apulian platform and South Adriatic Basin. The relative movement of the Adriatico-Apulian sub-plate between, the Euro Asiatic and African plates during from the Mesozoic to the Tertiary period, mainly controlled the tectonic evolution of the Albanides. The Ionian zone consists of anticline belts (Berati, Kurveleshi and Cika), that are overthrust toward the west with an amplitude about 20-30 km Their overthrustings was realized through regional sliding evaporitic horizons, which caused the masking of folded structures in the subthrust, with the perspective plays.
The Kurveleshi anticlinal belt represents a mega-anticlinal with a length of 210 km and a width of about 20 km, and it is characterized by anticline structures with heterogeneous dimensions, predominantly those of great dimensions and linear type. The overthrusting of the anticline units has a local character, and it is more developed in the Kurveleshi anticlinal belt. Its magnitude is about 8-10 km. As a result of these overthrusts, imbrication and duplex styles are formed, leadind to the masking of the subthrust complex with structures of large interest (e.g. Delvina, Karbunara, etc.) where two oil fields have been dioscovered beneath the Mali Gjere anticline (Delvina oil field) and the Kremenara anticline (Karbunara oil field). Backthrust faults phenomena are secondary and they taken place in the post-collision stage. Generally they are easterward thrust faults of structural units with an amplitude of 5-10 km. The Kurveleshi anticlinal belt, based on tectonic features, is divided into two parts: The southern part, from Qafa Sevaster in the north down to Greece to the south. and northern part, from Qafa Sevaster in the south up to the end of the Patos-Verbas structure.
In the southern part these features predominate: The anticline structures are large in size, and overthrust with a large amplitude (8-10 km) westward. The evaporitic diapirs have erupted through local faults of the anticline structures of the Kurveleshi anticlinal belt (Mali Gjere, Kurveleshi and Fterra anticlines). These eruptions (Delvina, Picar-Kapariel-Bashaj, etc.) have helped in the overthrusting of these structural units. It must be mentioned that the backthrusting is also affected by the diapir action. Moreover, vertical diapir occur, in the center of the structures like Navarica. In the northern part, the anticline structures are generally small to medium in size. Only the Patos-Verbas anticline is larger in size. In the Kurveleshi anticlinal belt the Ballsh and Visoka oilfields have developed. The eastern flank of the Shushica synclinal belt apears folded, and the carbonate anticline structures have developed. Existing oil fields include the Gorisht-Kocul, Cakran-Moallaj-Kreshpan and Amonica. These oil fields shoud continue towards the north (under the overthrust of the Patos-Verbas antcline) and in the south (under the regional ovethrust of the Kuervelesh anticlinal belt).
Introducing the novel technique for enhancing oil recovery from available petroleum reservoirs is one of the important issues in future energy demands. Among of all operative factors, wettability may be the foremost parameter affecting residual oil saturation in all stage of oil recovery. Although wettability alteration is one of the methods which enhance oil recovery from the petroleum reservoir. Recently, the studies which focused on this subject were more than the past and many contributions have been made on this area. The main objective of the current study is experimentally investigation of the two nonionic surfactants effects on altering wettability of reservoir rocks. Purpose of this work is to change the wettability to preferentially the water-wet condition. Also reducing the residual oil saturation (Sor) is the other purpose of this work. The wettability alteration of reservoir rock is measured by two main quantitative methods namely contact angle and the USBM methods. Results of this study showed that surfactant flooding is more effective in oil-wet rocks to change their wettability and consequently reducing Sor to a low value. Cedar (Zizyphus Spina Christi) is low priced, absolutely natural, and abundantly accessible in the Middle East and Central Asia. Based on the results, this material can be used as a chemical surfactant in field for enhancing oil recovery.
Changqing old oilfield Jurassic reservoir's average calibration recovery is 24.7%, with geological reserves recovery of 16.6%, water cut of 65.2%. And most of Jurassic reservoirs are in the middle and later field life, part of them has entered the high water cut and high recovery stage. Traditional water flooding way for improving oil recovery becomes more difficult, and new method has to be considered. Maling oilfield BS district is a typical representative, with high water cut of 90.8%, high recovery percent of 26.1% and low oil recovery rate of 0.25%. To explore the new way to improve oil recovery, the polymer and surfactant (SP for short) important pilot test has been developed. The low permeability reservoir indoor core data in high water cut stage and inspection well results indicate that the reservoir permeability, pore combination characteristics and pore type changed greatly after long-term water flooding development. These changes bring more difficulties to the continue development, especially the high injection pressure, which can cause other problems for well pattern infilling and EOR. This paper takes the high injection pressure problem of Maling BS district Jurassic reservoir for example, analyzes the physical property change law on the following aspects: the development mode in the past, core analysis, formation sensitivity, interstitial matter, well test interpretation results, in order to help to further effective development and provide important parameters for tertiary oil recovery technique for similar reservoirs and others.
Knowledge about reservoir fluid properties such as bubble point pressure (Pb) plays a vital role in improving reliability of oil reservoir simulation. In this work, hybrid of swarm intelligence and artificial neural network (ANN) as a robust and effective method was executed to determine the Pb of crude oil samples. In addition, the exactly precise Pb data samples reported in the literatures were employed to create and validate the PSO-ANN model. To prove and depict the reliability of the smart model developed in this study for estimating Pb of crude oils, the conventional approaches were applied on the same data set. Based on the results generated by PSO-ANN model and other conventional methods and equation of states (EOS), the PSO-ANN model is a reliable and accurate approach for estimating Pb of crude oils. This is certified by high value of correlation coefficient (R2) and insignificant value of average absolute relative deviation (AARD%) which are obtained from PSO-ANN outputs. Outcomes of this study could help reservoir engineers to have better understanding of reservoir fluid behavior in absence of reliable and experimental data samples.
Application of non-Newtonian Power-law fluids (e.g. polymeric solutions) for production enhancement in petroleum reservoirs has increased over the last three decades. These fluids are often injected as viscous solutions to improve mobility ratio and enhance oil recovery during chemical flooding. As part of the flooding operation, surfactant (or micellar) solutions are first injected at the leading edge of the flood to reduce interfacial tension between water and oil. Subsequently, a slug of polymer solution is injected ahead of normal water to increase viscosity of the water, improve volumetric sweep efficiency and accelerate oil production. Analysis of pressure tests conducted pre and post injection, to evaluate mobility of these fluids, is more demanding than conventional techniques, which were developed strictly for Newtonian fluids. In naturally-fractured reservoirs, flow of non-Newtonian fluids is more complex due to fracture-matrix interaction which is usually resonated in the pressure footprints. Some models have been developed to aid interpretation of pressure tests, but boundary effects on down-hole measurements due to structural discontinuity and presence of an active aquifer, have not been thoroughly investigated.
This article presents an analytic technique for interpreting pressure falloff tests of non-Newtonian Power-law fluids in wells that are located near boundaries in dual-porosity reservoirs. First, dimensionless pressure solutions are obtained and Stehfest inversion algorithm is used to develop new type curves. Subsequently, long-time analytic solutions are presented and interpretation procedure is proposed using direct synthesis. Two examples, including real field data from a heavy oil reservoir in Colombian eastern plains basin, are used to validate and demonstrate application of this technique. Results agree with conventional type-curve matching procedure. The approach proposed in this study avoids the use of type curves, which is prone to human errors. It provides a better alternative for direct estimation of formation and flow properties from falloff data.
This research studies the motion of immiscible two-phase liquid flow in a capillary tube through a numerical approach employing the volume of fluid method, for simulating the core-annular flow and water flooding in oil reservoirs of porous media. More specifically, the simulations are a representation of water flooding at a pore scale. A capillary tube model is established with ANSYS Fluent and verified. The numerical results matches well with the existing data available in the literature. Penetration of a less viscous liquid in a liquid of higher viscosity and the development of a residual wetting film of the higher viscosity liquid are thoroughly investigated. The effects of Capillary number, Reynolds Number and Viscosity ratio on the residual wetting film are studied in detail, as the thickness is directly related to the residual oil left in the porous media after water flooding. It should be noticed that the liquids considered in this research can be any liquids of different viscosity not necessarily oil and water. The results of this study can be used as guidance in the field of water flooding.
Aquifers, which play a prominent role as an effective tool to recover hydrocarbon from reservoirs, assist the production of hydrocarbon in various ways. In so-called water flooding methods, the pressure of the reservoir is intensified by the injection of water into the formation, increasing the capacity of the reservoir to allow for more hydrocarbon extraction. Some studies have indicated that oil recovery can be increased by modifying the salinity of the injected brine in water flooding methods. Furthermore, various characteristics of brines are required for different calculations used within the petroleum industry. Consequently, it is of great significance to acquire the exact information about PVT properties of brine extracted from reservoirs. The properties of brine that are of great importance are density, enthalpy, and vapor pressure. In this study, radial basis function neural networks assisted with genetic algorithm were utilized to predict the mentioned properties. The root mean squared error of 0.270810, 0.455726, and 1.264687 were obtained for reservoir brine density, enthalpy, and vapor pressure, respectively. The predicted values obtained by the proposed models were in great agreement with experimental values. In addition, a comparison between the proposed model in this study and a previously proposed model revealed the superiority of the proposed GA-RBF model.
The application of distributed temperature sensors (DTS) to monitor producing zones of horizontal well through a real-time measurement of a temperature profile is becoming increasingly popular. Those parameters, such as flow rate along wellbore, well completion method, skin factor, are potentially related to the information from DTS. Based on mass-, momentum-, and energy-balance equations, this paper established a coupled model to study on temperature distribution along wellbore of fracturing horizontal wells by considering skin factor in order to predict wellbore temperature distribution and analyze the factors influencing the wellbore temperature profile. The models presented in this paper account for heat convective, fluid expansion, heat conduction, and viscous dissipative heating. Arriving temperature and wellbore temperature curves are plotted by computer iterative calculation. The non-perforated and perforated sections show different temperature distribution along wellbore. Through the study on the sensitivity analysis of skin factor and flow rate, we come to the conclusion that the higher skin factor generates larger temperature increase near the wellbore, besides, temperature along wellbore is related to both skin factors and flow rate. Temperature response type curves show that the larger skin factor we set, the less temperature augmenter from toe to heel could be. In addition, larger flow rate may generate higher wellbore temperature.
During the long-time operation of salt rock storage cavern, between its formations, damaged interfaces induced by discontinuous creep deformations between adjacent layers will possibly lead to serious gas leakage. In this paper, damaged interfaces are considered as main potential leakage path: firstly in meso-level, gas flow rule along the interface is analyzed and the calculation of equivalent permeability is discussed. Then based on porous media seepage theory, gas leakage simulation model including salt rock, cavity interlayers and interface is built. With this strategy, it is possible to overcome the disadvantage of simulation burden with porous-fractured double medium. It also can provide the details of gas flowing along the damaged zones. Finally this proposal is applied to the salt cavern in Qianjian mines (East China). Under different operation pressures, gas distributions around two adjacent cavities are simulated; the evolvement of gas in the interlayers and salt rock is compared. From the results it is demonstrated that the domain of creep damage area has great influence on leakage range. And also the leakage in the interface will accelerate the development of leakage in salt rock. It is concluded that compared with observations, this new strategy provides closer answers. The simulation result proves its validity for the design and reasonable control of operating pressure and tightness evaluation of group bedded salt rock storage caverns.
The fissures and rock bridges with different dips had different contributions to crack's initiation, propagation, convergence and penetration. In this paper, based on the rock fracture theory, the crack's propagation and evolution process on rock specimen with double fissures under uniaxial compression was simulated. As a result, the crack propagation and evolution law of rocks with different fissure dips (α = 0°, 15°, 30°, 45°, 60°, 75°, 90°; β = 45°) and different rock bridge dips (β = 0°, 30°, 45°, 60°, 90°; α = 45°) was obtained by numerical tests. Meanwhile, the fissure and rock bridge dips influence on the macro mechanical properties of rock was analyzed. Besides, the paper investigated the influences of different fissure dips and different rock bridge dips on the bridge transfixion. The study is of great significance to reveal the impact of different dips on the mechanical mechanism of multiple-fissures rock under specific conditions, and it also has important theoretical significance for the research on multiple-fissure rock.
Stick-slip vibration presents one of the major causes of drilling problems, such as premature tool failures, low drilling efficiency and poor wellbore quality. The objective of this work is to investigate the influences of rotary table speed (RTS) on stick-slip phenomenon of the drilling system. In this study, the drilling system is treated as a lumped torsional pendulum model of which the bit/rock interaction is regarded as Coulomb friction. By analyzing cases with different RTS, two types of vibrations on the bit are found: stick-slip vibration and uniform motion. With an increase in the RTS, the stick-slip vibration on the drill bit disappears once the RTS arrives at its critical value. For the cases that stick-slip vibrations occur, the phase trajectories converge toward a limit cycle. For the cases that stick-slip vibration does not appear, the drill bit tends to stabilize at a uniform motion and the phase trajectories correspond to contracting spirals observed in the phase plane.
Bearings are key components of cone bit, thus its rapid failure is a major cause of leading to lower life of the bit. To improve the bearing performance and prolong working life, contact mechanics of hollow cylindrical roller bearing of cone bit was simulated. Effects of hollow size, drilling pressure, friction coefficient and fitting clearance on mechanics performance of the bearing were studied. The results show that the maximum equivalent stress of the hollow cylindrical roller bearing appears on the claw journal, and the maximum contact stress appears on the contact pair of the hollow roller. Besides, hollow sizes have a greater impact on the equivalent stress and contact stress of the cylindrical roller, while the influence on the stress of the cone and claw journal is relatively small. With the increasing of the drilling pressure and fitting clearance, equivalent stress and contact stress of bearing parts increase. The friction coefficient has little impact on mechanical performance of the bearing. As the 121/4SWPI517 type hollow cylindrical roller bearing of cone bit an example, the optimal hollow size is 55%, the drilling pressure is 140 kN and the fitting clearance is 0-0.02 mm.